1. Field of the invention
The present invention concerns a lighting device adapted to produce a spot of homogeneously colored light with the intensity and color adjustable at the same time.
One particularly advantageous application of this type of device is to stage lighting although, generally speaking, any situation entailing recourse to colored lighting may constitute an application of the present invention.
For example, the invention may be applied to film and photographic lights.
2. Description of the prior art
When it is required to light a particular area and at the same time to color it in a particular way, it is known practise to illuminate the area using a plurality of combined light sources.
More specifically, obtaining a specific coloration in a localized spot of light in conjunction with a particular luminous intensity is usually achieved by arranging for a plurality of uniformly colored light beams to converge on the spot, each beam being in one fundamental color, so that by appropriately adjusting these fundamental colors the required color may be obtained.
The relative adjustment of the fundamental colors is usually obtained by individually adjusting the luminous intensity of each source.
This relative adjustment of the intensity of the sources is combined with an overall adjustment of luminous intensity in order to obtain the required intensity of illumination within the spot, in addition to the required color.
The light sources, which are usually spotlights, are spaced from each other and adjusted individually.
This has numerous disadvantages:
There must be many operators sufficiently skilled to aim the various sources simultaneously towards the same subject to be lit and at the same time to adjust the luminous intensity of each spotlight according to the color required and the overall luminous intensity required.
As an alternative to this, the spotlights might be remote controlled, using electric motors, for example, although remote control systems enabling both the orientation and the luminous intensity to be adjusted at the same time are complex and costly.
It is also a frequent requirement to obtain a number of spots of light at different places simultaneously.
Also, the subjects to be lit are often moving. It is then necessary to track them by simultaneous and appropriate orientation of the spotlights. As the spotlights are not disposed at the same location, for reasons of size and mobility, it is a relatively complex task to track a moving subject, especially when using simultaneous remote control.
In practise, the angles of incidence relative to the subject of the spotlights whose beams are combined in order to obtain the required coloration of the resulting spot are sufficiently different to create a non-homogenous spot.
Each spotlight creates a spot, which is generally substantially oval because of the obliqueness of the beam relative to the plane in which the subject is moving, and the spots cannot be superimposed exactly, for the reasons given above.
The most advantageous solution to this problem consists in carrying out the required mixing of colors in a single spotlight or, more generally, on the path of propagation of a light beam.
A solution of this kind has already been envisaged and is described in French patent No. 2,546,271 published 11/1984.
This solution provides a spotlight comprising a light source, means for conferring on the light source a definite propagation direction, so defining a beam, and means for adjusting the width, intensity and color of the beam.
The beam is colored by inserting into its path a plurality of colored filters comprising films of colored transparent material, the term of art for which is "gelatins", each colored filter being placed over a greater or lesser part of the transverse cross-section of the beam.
Thus according to the proportion of colored surfaces inserted into the light beam by each filter relative to the overall surface area of the cross-section of the beam at the level of the filter, there is obtained a density of coloration in the color of the appropriate filter depending on the adjustment applied.
In practise it has been found necessary to implement each filter in two parts movable in a plane normal to the light beam, the two parts of each filter joining completely in one extreme position and being able to occupy all intermediate positions between this and another extreme position in which they are moved apart so as to no longer intersect the light beam.
Although constituting a significant advance relative to the prior art, the resulting colored light spots lack homogeneity.
The explanation for this is as follows: when a filter partly colors the light beam, being inserted into a defined part of the surface area of the transverse cross-section of the beam, it colors precisely one part of this surface area.
This means that one part of this cross-section is totally colored by the filter, whereas the remaining part of the surface is not colored at all by this filter.
For example, if 40% only of the beam cross-section is colored red, 40% of the beam cross-section will be totally red and the remainder totally white.
This will be noticeable in the spot of light illuminating the subject, which is not the required result.
What is wanted, in the specific case of the example just mentioned, is a spot colored 40% red over all of its surface area, homogeneously.
The object of the present invention is to make it possible to color homogeneously a spot of light from a lighting device colored to the required shade, this shade being adjustable at will.